C.35: A base class destructor should be either public and virtual, or protected and nonvirtual

基類(lèi)的析構(gòu)函數(shù)要么是公開(kāi)的虛函數(shù)，要么是保護(hù)的非虛函數(shù)

Reason(原因)

To prevent undefined behavior. If the destructor is public, then calling code can attempt to destroy a derived class object through a base class pointer, and the result is undefined if the base class's destructor is non-virtual. If the destructor is protected, then calling code cannot destroy through a base class pointer and the destructor does not need to be virtual; it does need to be protected, not private, so that derived destructors can invoke it. In general, the writer of a base class does not know the appropriate action to be done upon destruction.

為了避免無(wú)定義的行為。如果析構(gòu)函數(shù)是公有的，那么調(diào)用側(cè)的代碼就會(huì)嘗試使用基類(lèi)指針?shù)N毀派生類(lèi)的對(duì)象，在基類(lèi)的析構(gòu)函數(shù)為非虛函數(shù)時(shí)其結(jié)果時(shí)沒(méi)有定義的。如果析構(gòu)函數(shù)時(shí)保護(hù)的，那么調(diào)用側(cè)代碼就無(wú)法通過(guò)基類(lèi)類(lèi)型指針?shù)N毀派生類(lèi)對(duì)象，這是析構(gòu)函數(shù)就沒(méi)有必要一定是虛函數(shù)。析構(gòu)函數(shù)是保護(hù)而不是私有的，這樣派生類(lèi)的析構(gòu)函數(shù)才能調(diào)用它。通常，基類(lèi)的設(shè)計(jì)者不會(huì)知道在析構(gòu)函數(shù)中應(yīng)該執(zhí)行什么樣的動(dòng)作。

Discussion(討論)

See this in the Discussion section：參見(jiàn)討論章節(jié)：

https://github.com/isocpp/CppCoreGuidelines/blob/master/CppCoreGuidelines.md#Sd-dtor.

Example, bad(反面示例)

struct Base { // BAD: implicitly has a public nonvirtual destructor
virtual void f();
};
struct D : Base {
string s {"a resource needing cleanup"};
~D() { /* ... do some cleanup ... */ }
// ...
};
void use()
{
unique_ptr p = make_unique();
// ...
} // p's destruction calls ~Base(), not ~D(), which leaks D::s and possibly more

Note(注意)

A virtual function defines an interface to derived classes that can be used without looking at the derived classes. If the interface allows destroying, it should be safe to do so.虛函數(shù)定義了派生類(lèi)的接口，它可以在不關(guān)注派生類(lèi)的情況下使用。如果接口允許對(duì)象，那么這個(gè)銷(xiāo)毀過(guò)程應(yīng)該是安全的。

Note(注意)

A destructor must be nonprivate or it will prevent using the type:析構(gòu)函數(shù)必須是非私有的，除了它不想被別人用。(這樣可以由類(lèi)自己控制銷(xiāo)毀，譯者注)

class X {

~X(); // private destructor
// ...
};
void use()
{
X a; // error: cannot destroy
auto p = make_unique(); // error: cannot destroy
}

Exception(例外)

We can imagine one case where you could want a protected virtual destructor: When an object of a derived type (and only of such a type) should be allowed to destroy another object (not itself) through a pointer to base. We haven't seen such a case in practice, though.我們可以想象一種需要保護(hù)的虛函數(shù)析構(gòu)函數(shù)的情況：當(dāng)希望允許派生類(lèi)的對(duì)象(只有這個(gè)類(lèi)型)通過(guò)基類(lèi)指針?shù)N毀另外一個(gè)對(duì)象(不是它自己)時(shí)。但是我們還沒(méi)有在實(shí)際的開(kāi)發(fā)中遇到這種情況。

Enforcement(實(shí)施建議)

• A class with any virtual functions should have a destructor that is either public and virtual or else protected and nonvirtual.
• 擁有虛函數(shù)的類(lèi)的虛函數(shù)要么是公開(kāi)的虛函數(shù)，要么是保護(hù)的非虛函數(shù)。

譯者注：擁有虛函數(shù)一般就意味著它有派生類(lèi)。

原文鏈接：

https://github.com/isocpp/CppCoreGuidelines/blob/master/CppCoreGuidelines.md#c35-a-base-class-destructor-should-be-either-public-and-virtual-or-protected-and-nonvirtual

---

覺(jué)得本文有幫助？請(qǐng)分享給更多人。

更多文章請(qǐng)關(guān)注微信公眾號(hào)【面向?qū)ο笏伎肌?#xff01;

面向?qū)ο箝_(kāi)發(fā)，面向?qū)ο笏伎?#xff01;

創(chuàng)作挑戰(zhàn)賽新人創(chuàng)作獎(jiǎng)勵(lì)來(lái)咯，堅(jiān)持創(chuàng)作打卡瓜分現(xiàn)金大獎(jiǎng)

總結(jié)

以上是生活随笔為你收集整理的unique函数_C++核心准则C.35:基类的析构函数必须满足的条件的全部?jī)?nèi)容，希望文章能夠幫你解決所遇到的問(wèn)題。

如果覺(jué)得生活随笔網(wǎng)站內(nèi)容還不錯(cuò)，歡迎將生活随笔推薦給好友。